This invention relates to braided tubular objects and more especially to braided tubular gaskets exhibiting excellent thermal performance. The invention also relates to apparatus and method for the production of such articles.
Braided tubular gaskets incorporating insulating yarns and resilient wire have been in wide spread use for many years. Oven door gaskets are a particular application for such tubular articles. A particularly effective tubular gasket of the kind referred to is manufactured by Federal-Mogul Systems Protection Group, Inc. under the trademark PYROSEAL. These gaskets comprise an inner support layer of knitted wire which resiliently supports an outer layer of relatively densely braided glass fiber yarn or other yarn characterized by good thermal performance. In such gaskets, the relatively densely braided thermal yarn effectively insulates the oven door and the wire resiliently supports the yarn so that a very effective seal is provided.
More recently, tubular oven gaskets have been produced in which the wire and the glass are interbraided. In these gaskets, the proportion of wire to glass can be adjusted to provide the requisite resilience combined with thermal performance. The interbraiding of the wire and the glass eliminates a processing step and yields a satisfactory gasket for many purposes at a substantial savings in cost. As in the PYROSEAL(copyright) gasket, wire provides a support matrix within which the spaced attachment protrusions are held in place.
One problem with gaskets of the kind just mentioned is that the same thermal performance achievable with the PYROSEAL(copyright) gasket has not been found to be practical due to limitations in the braiding process as carried out with conventional circular braiding equipment. Since the relatively fine diameter wire used in such gaskets has a tendency to cut the glass during the braiding process, it has been found necessary to feed the yarn and the glass from separate bobbins on separate carriers. In a conventional circular braider, when the wire occupies a separate carrier, in the tubular gasket produced, insulating yarn is replaced by small diameter wire. When one inspects a gasket made by this method of interbraiding, the points where wires cross over one another create relative large openings in the surface of the gasket which are destructive of good thermal protection. Even if the amount of wire used in the gasket is limited, thermal performance is sacrificed.
An objective of the invention is the braiding of tubular articles comprised of yarns of different properties, particularly yarns of different abrasive properties in a manner which reduces porosity and the tendency of the more abrasive yarn to abraid and break the less abrasive yarn during the braiding process. The invention is particularly concerned with the production of tubular gaskets comprised of interbraided wire and glass or other insulating yarn having thermal performance equivalent to gaskets comprising a knitted wire core with a braided cover layer. This objective achieved by the use of yarn carriers, each supporting multiple superimposed yarn packages. The carriers of the present invention include a yarn support spindle sized to receive a bobbin of relatively large diameter yarn of standard size. A second support spindle is provided to receive a bobbin of relatively fine diameter material, such as flexible resilient monofilament wire having the same length as the length of the yarn on the first bobbin. Preferably, the second bobbin is oriented transversely to the axis of rotation of the first bobbin, and the spindle upon which it is supported is short relatively to the length of the spindle for the first bobbin. Independent yarn tensioning means are provided for the material fed from the two bobbins. The yarns are simultaneously delivered to the fell through separate guides which hold them in spaced apart relationship so that the relatively thin, hard material cannot abraid the fragile fibers of the insulating material during the braiding process.
Through the use of this equipment, the production advantage of producing gaskets having interbraided wire or other fine diameter filamentary material along with relatively large diameter fibrous yarns is achieved without sacrificing thermal performance. The tubular articles so produced are relatively less porous since every braider carrier delivers at least one relatively large diameter yarn to the finished article.
Yet another advantage of the invention arises due to the compact nature of the stacked carrier. The yarn packages mounted on the stacked carrier may be of the same capacity as the yarn packages located on the single carriers and may have the same capacity as the carriers of the fine diameter material without occupying more space of the braider deck. An advantage of this is that neither carrier of the double carriers will prematurely run out of yarn, thereby avoiding premature stoppage of the braider.
A further aspect of the invention is a method of braiding an insulating sleeve, such as a thermal gasket, comprising loading the deck of a circular braider with a first set of yarn carriers, each carrying a single yarn package of an insulating yarn and establishing a first set of yarn positions occupied by the insulating yarn. The method further comprises selectively positioning a second set of yarn carriers on the braider deck, each carrying a yarn package of insulating yarn and a second package of resilient wire, thereby establishing a second set of yarn positions, the second set of yarn positions being occupied by the insulating yarn and the wire. The method includes the step of interbraiding the yarn of the first set of yarn carriers with the yarn and wire of the second set of yarn carriers and further comprises separately and simultaneously guiding the yarn and the wire from the yarn and wire packages of the carriers of the second set of carriers. Still further, the method preferably comprises axially orienting the package of insulating yarn on a carrier of the second set transversely of the axis of the wire package on the carrier.
In yet another of its aspects, the invention comprises the manufacture of a tubular gasket of insulating yarn interbraided with resilient wire, wherein the sleeve has insulating yarn and wire combined at selected yarn positions and insulating yarn exclusively at the remaining yarn positions. Preferably, the yarn and wire are densely packed so as to restrict openings for the passage of air through the braided structure. An insulating tubular gasket according to the invention preferably comprises insulating yarn having a denier of between about 1800 to about 8000 and wire in monofilament form having a diameter of between about 0.004xe2x80x3 and about 0.007xe2x80x3.